A conventional aircraft gas turbine engine includes a rotating fan having a plurality of circumferentially spaced fan blades removably mounted to a rotor. In one form, the rotor includes a disk having an outer rim and an inner hub with a radially extending web therebetween. The rim includes a plurality of circumferentially spaced, axially extending dovetail grooves for receiving axial dovetails of the fan blades for supporting the fan blades as they rotate with the disk.
A conventional rim has a width in the axial direction selected for ensuring acceptably low stress in the rim due to centrifugal loads imposed by the rotating blades on the rim. The width of the web is relatively smaller than that of the rim for minimizing weight of the disk, and the width of the hub is relatively larger than that of the web and may be up to about the width of the rim for providing suitable structural integrity of the entire disk.
Since the fan assembly has the largest outer diameter of the rotating blade rows of a conventional turbofan aircraft gas turbine engine, it typically has relatively high rotational energy due to centrifugal force or load generated thereby during operation. The larger the fan blades, the higher the potential centrifugal loads, and, therefore, the fans are typically run at relatively low rotational speeds to reduce the centrifugal loads so that stress generated thereby in the disk is below acceptable limits for obtaining a suitable useful life of the disk and avoiding catastrophic failure during operation.
Conventional rotor disks are known to fail due to propagating cracks under relatively high centrifugal loads. Cracks typically form at stress concentrations in the disk such as, for example, undetected inclusions in the disk, or at stress risers such as holes in the disk. Cracks may propagate circumferentially around the disk and may result in the rim separating from the web in one failure mode. In another failure mode, cracks may propagate in the radial direction through the hub, web, and rim thusly radially splitting the disk and resulting in failure.
Disks, therefore, are conventionally designed for obtaining limited stress therein due to centrifugal loads to reduce the likelihood of failure and for providing an acceptable service life. The disks may also be constructed in the form of a multi-disk assembly for spreading the centrifugal load between the respective disks so that failure of one disk does not result in failure of the entire multi-disk assembly.
In one exemplary turbofan engine, large fan blades are provided having a height of about 1 meter with the diameter of the fan assembly measured to the blade tips of about 3 meters. The fan rotates at about 2300 rpm, thusly resulting in substantial centrifugal loads imparted from the blades into the supporting rotor assembly. Accordingly, in order to prevent catastrophic failure of the rotor assembly having such relatively high centrifugal loads, an improved rotor assembly is desired which will prevent such failure and provide an indication of the onset of such failure in order to effect appropriate remedial action. Furthermore, in view of the relatively large centrifugal loading in such a fan, a simpler and more structurally efficient rotor assembly having reduced structural mass and reduced stress risers is desired.